[英]Use sf polygon object as window in spatstat
Hello all potential helpers,你好所有潜在的帮助者,
I have a SpatialPolygonDataFrame
object obtained from the tigris
package and I would like to use it as a polygonal window in the creation of a ppp
object.我有一个从
tigris
包获得的SpatialPolygonDataFrame
对象,我想在创建ppp
对象时将它用作多边形窗口。 Here is what I tried:这是我尝试过的:
# Needed packages
library(spatstat)
library(sf)
# Download geospatial data for Lee county in Alabama (home of the great Auburn University by the way!)
county <- tigris::county_subdivisions(state = "Alabama", county = "Lee")
# The polygon of Lee county is subdivided, so I convert it to a single polygon after converting it to an sf object
county_sf <- st_as_sf(county)
county_one <- st_union(county_sf)
# A quick plot of the object outputs what I am expecting
plot(county_one)
# Now I create a planar point pattern and I use county_one as the window
p <- ppp(x = -85.4, y = 32.5, window = as.owin((county_one)))
# But the plot here shows that the window is just a rectangle and not the polygon :(
plot(p)
Thank you for your help.感谢您的帮助。
Note: I have edited this answer to contain full details.注意:我已编辑此答案以包含完整的详细信息。
As @TimSalabim mentions this is under way in sf
, but until then you have to go through the old sp
classes such as SpatialPolygons
.正如@TimSalabim 提到的,这是在
sf
,但在那之前你必须通过旧的sp
类,如SpatialPolygons
。 Use something like as_Spatial
in sf
and then load maptools
and use as.owin
or as(x, "owin")
on the Spatial
object.在
sf
使用类似as_Spatial
东西,然后加载maptools
并在Spatial
对象上使用as.owin
或as(x, "owin")
as.owin
as(x, "owin")
。
Furthermore, you can only use coordinates in planar (projected) space with spatstat
and not coordinates on the curved surface of the earth.此外,您只能使用带有
spatstat
平面(投影)空间中的坐标,而不能使用地球曲面上的坐标。 You have to project to a relevant planar coordinates system.您必须投影到相关的平面坐标系。 Maybe <epsg.io/6345> is usable in this case.
也许 <epsg.io/6345> 在这种情况下可用。 To project to this coordinate system use
sf::st_transform(county_one, crs = 6345)
.要投影到此坐标系,请使用
sf::st_transform(county_one, crs = 6345)
。 Afterwards you convert to Spatial
and then owin
.之后,您转换为
Spatial
,然后owin
。 Note: Choosing the relevant projection is a science, and I don't know much about it, so do a bit of research if you want to make sure you don't get too distorted results.注意:选择相关投影是一门科学,我对它了解不多,所以如果你想确保你不会得到太扭曲的结果,那么做一些研究。
Specifically with the original example you can do:特别是使用原始示例,您可以执行以下操作:
# Needed packages
library(spatstat)
#> Loading required package: spatstat.data
#> Loading required package: nlme
#> Loading required package: rpart
#>
#> spatstat 1.62-2 (nickname: 'Shape-shifting lizard')
#> For an introduction to spatstat, type 'beginner'
library(sf)
#> Linking to GEOS 3.8.0, GDAL 3.0.2, PROJ 6.2.1
library(maptools)
#> Loading required package: sp
#> Checking rgeos availability: TRUE
library(tigris)
#> To enable
#> caching of data, set `options(tigris_use_cache = TRUE)` in your R script or .Rprofile.
#>
#> Attaching package: 'tigris'
#> The following object is masked from 'package:graphics':
#>
#> plot
county <- county_subdivisions(state = "Alabama", county = "Lee", class = "sf", progress_bar = FALSE)
county_one <- st_union(county)
plot(county_one)
county_flat <- st_transform(county_one, crs = 6345)
plot(county_flat)
county_owin <- as.owin(as_Spatial(county_flat))
100 random points in the county:县内100个随机点:
p <- runifpoint(100, win = county_owin)
plot(p)
just want to note here that coercion methods for sf classes are now registered (if that's the right word) by the sf package.只是想在这里注意 sf 类的强制方法现在由 sf 包注册(如果这是正确的词)。 I don't fully understand the R magic that finds methods, but it does work.
我并不完全理解 R 寻找方法的魔法,但它确实有效。
library(sf)
library(spatstat)
> methods(as.owin)
[1] as.owin.boxx as.owin.data.frame as.owin.default as.owin.distfun
[5] as.owin.dppm as.owin.funxy as.owin.im as.owin.influence.ppm
[9] as.owin.kppm as.owin.layered as.owin.leverage.ppm as.owin.linfun
[13] as.owin.linnet as.owin.lintess as.owin.lpp as.owin.lppm
[17] as.owin.msr as.owin.MULTIPOLYGON* as.owin.nnfun as.owin.owin
[21] as.owin.POLYGON* as.owin.ppm as.owin.ppp as.owin.psp
[25] as.owin.quad as.owin.quadratcount as.owin.quadrattest as.owin.rmhmodel
[29] as.owin.sf* as.owin.sfc* as.owin.sfc_MULTIPOLYGON* as.owin.sfc_POLYGON*
[33] as.owin.SpatialGridDataFrame* as.owin.SpatialPixelsDataFrame* as.owin.SpatialPolygons* as.owin.tess
see '?methods' for accessing help and source code
So, assuming you have properly projected your data (as noted by @Ege Rubak), calling as.owin
directly should work:因此,假设您已正确投影数据(如@Ege Rubak 所述),直接调用
as.owin
应该可以工作:
library(tigris)
county <- county_subdivisions(state = "Alabama",
county = "Lee",
class = "sf",
progress_bar = FALSE)
county <- st_union(county)
county <- st_transform(county, crs = 6345)
window <- as.owin(county)
plot(window)
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